MADRID -- Testifying in the first-ever criminal proceeding against a member of Spain's royal family, the king’s youngest daughter Saturday denied involvement in her husband’s business dealings, lawyers said following the lengthy closed-door session.

The princess, Infanta Cristina, and her husband, former Olympian-turned-businessman Iñaki Urdangarin, are under investigation for possible tax fraud and money-laundering. Their legal woes have sent the Spanish royal family's approval rating to all-time lows amid soaring unemployment and calls for 76-year-old King Juan Carlos to abdicate.

About 200 protesters whistled and chanted slogans against the monarchy and corruption as the princess, 48, was chauffeured in a small Ford hatchback before walking the last few yards into the courthouse Saturday on the Spanish island of Mallorca. She smiled at the crowd but did not wave, and mumbled, “Hasta luego, gracias!” to those still gathered at the end of the day.

“Her smile says it all,” Cristina's lawyer Miquel Roca told reporters. “We're satisfied justice will be done. We are all equal before the law, and the princess has proven that,” he said, calling the session “extensive and exhaustive.”

An independent lawyer said Cristina told the judge that she “trusted in her husband” but was not privy to the day-to-day details of his business dealings. And she was evasive in response to many questions, said Manuel Delgado, lawyer for the group Frente Civico, which filed an independent complaint against the princess.

A two-time Olympic handball bronze medalist, Urdangarin reinvented himself as a sports entrepreneur after his 1997 marriage to Cristina. He started the now-defunct Noos Foundation, a nonprofit group that organized sports events and conventions -- through which he is accused of embezzling $8 million in public donations. The princess was on Noos' board of directors.

Prosecutors suspect Urdangarin and a business partner, Diego Torres, set up shell companies through which to launder money. Tax documents show that the princess was cosigner and 50% owner of at least one of those companies, a real estate firm called Aizoon, which allegedly paid for renovations to the couple's $8-million Barcelona mansion and other personal expenses, tax-free. Torres is also under investigation.

Saturday's court session was similar to a U.S. grand jury hearing. Judge José Castro will decide whether to formally charge the princess, who could face up to six years in prison and hefty fines if convicted of tax fraud and money-laundering. A parallel investigation is underway against Urdangarin, who also has not yet been charged.

Cristina was questioned for more than six hours Saturday by Castro, who has previously referred to Aizoon as a “front company.” The princess sat in a high-backed chair directly facing the judge. Behind him on the courtroom wall, hangs a huge picture of the princess' father, King Juan Carlos, the Spanish head of state.

Among Spaniards, Juan Carlos has long been admired for helping to install and safeguard democracy in Spain after the 1975 death of military dictator Gen. Francisco Franco, and putting down an armed coup in parliament in 1981. But in recent years his popularity has waned, in part because of a 2012 elephant-hunting trip he took in Africa, which cost many times the average Spaniard's annual salary, during a time of economic crisis.